1. Field of the Invention
This invention relates to automatic sheet feeding devices suitable for use with facsimile systems, optical read-out systems and other systems and apparatus that require automatic feeding of various types of sheets and notes, and more particularly it is concerned with an automatic sheet feeding device suitable for use in handling thin sheets, such as documents of small thickness or thin sheets with carbon backing, that have a high coefficient of friction.
2. Description of the Prior Art
In automatic sheet feeding devices for successively feeding one sheet after another from a stack of sheets by separating them to a desired operation station, each sheet is conveyed forwardly between feed rollers and respective friction members which are positioned against each other. When a plurality of sheets are delivered at a time to the feed rollers and friction members, they are separated from each other by the difference in the force of friction between the feed rollers, sheets and friction members. This sheet separation mechanism is simple in construction and used widely. However, this mechanism should be maintained with meticulous care so as to be in perfect operation condition at all times by keeping its components at a high degree of precision finishes, to enable the sheet feeding operation to be performed stably over a prolonged period of time without causing skewing of the sheets to occur.
A sheet feeding mechanism capable of performing sheet feeding stably over a prolonged period of time without the skew phenomenon is disclosed in Japanese Patent Laid-Open No. 88038/81, for example. In this sheet feeding mechanism, a stack of sheets set between the feed rollers and separation rollers are pushed back at the leading edge and reset following feeding of each sheet by the feed rollers from the stack of sheets, to thereby avoid skewing of the sheet fed by the feed rollers even if there is a sheet set in skew condition in the stack of sheets. Some difficulties would be experienced when this mechanism is used. Since the stack of sheets are pushed back between the feed rollers and separation rollers each time one sheet is fed by the feed rollers as aforesaid, misfeeding or feeding of a plurality of sheets might occur and the sheet fed might be wrinkled or deflected when the sheets handled are small in thickness, as is the case with documents of small thickness or thin sheets with carbon backing, because of their low rigidity. As a result, jaming of the sheets fed would occur. Particularly when the sheets handled are thin sheets with carbon backing, the carbon ink might adhere to surfaces of the rollers. When this phenomenon occurs, the force of friction exerted by the rollers would undergo changes and cause misfeeding or feeding of a plurality of sheets at a time to occur, and the carbon ink adhering to the surfaces of the rollers would stain the sheets fed by the feed rollers.